2,092 research outputs found
Thermal bistability through coupled photonic resonances
We present a scheme for achieving thermal bistability based on the selective
coupling of three optical resonances. This approach requires one of the
resonant frequencies to be temperature dependent, which can occur in materials
exhibiting strong thermo-optic effects. For illustration, we explore thermal
bistability in two different passive systems, involving either a periodic array
of Si ring resonators or parallel GaAs thin films separated by vacuum and
exchanging heat in the near field. Such a scheme could prove useful for thermal
memory devices operating with transition times hundreds of
milliseconds
Near-field thermal upconversion and energy transfer through a Kerr medium : Theory
We present an approach for achieving large Kerr --mediated
thermal energy transfer at the nanoscale that exploits a general coupled-mode
description of triply resonant, four-wave mixing processes. We analyze the
efficiency of thermal upconversion and energy transfer from mid- to
near-infrared wavelengths in planar geometries involving two slabs supporting
far-apart surface plasmon polaritons and separated by a nonlinear
medium that is irradiated by externally incident light. We study multiple
geometric and material configurations and different classes of interveening
mediums---either bulk or nanostructured lattices of nanoparticles embedded in
nonlinear materials---designed to resonantly enhance the interaction of the
incident light with thermal slab resonances. We find that even when the entire
system is in thermodynamic equilibrium (at room temperature) and under typical
drive intensities , the resulting upconversion
rates can approach and even exceed thermal flux rates achieved in typical
symmetric and non-equilibrium configurations of vacuum-separated slabs. The
proposed nonlinear scheme could potentially be exploited to achieve thermal
cooling and refrigeration at the nanoscale, and to actively control heat
transfer between materials with dramatically different resonant responses
Thermal radiation from optically driven Kerr () photonic cavities
We study thermal radiation from nonlinear () photonic cavities
coupled to external channels and subject to incident monochromatic light. Our
work extends related work on nonlinear mechanical oscillators [Phys. Rev. Lett.
97, 110602 (2006)] to the problem of thermal radiation, demonstrating that
bistability can enhance thermal radiation by orders of magnitude and result in
strong lineshape alternations, including "super-narrow spectral peaks"
occurring at the onset of kinetic phase transitions. We show that when the
cavities are designed so as to have perfect linear absorptivity (rate
matching), such thermally activated transitions can be exploited to
dramatically tune the output power and radiative properties of the cavity,
leading to a kind of Kerr-mediated thermo-optic effect. Finally, we demonstrate
that in certain parameter regimes, the output radiation exhibits Stokes and
anti-Stokes side peaks whose relative magnitudes can be altered by tuning the
internal temperature of the cavity relative to its surroundings, a consequence
of strong correlations and interference between the emitted and reflected
radiation
Near-field refrigeration and tunable heat exchange through four-wave mixing
We modify and extend a recently proposed four-wave mixing scheme [Opt.
Express 25 (19),23164 (2017)] for achieving near-field thermal upconversion and
energy transfer, to demonstrate efficient thermal refrigeration at low
intensities W/m over a wide range of gap sizes (from tens to
hundreds of nanometers) and operational temperatures (from tens to hundreds of
Kelvins). We further exploit the scheme to achieve magnitude and directional
tunability of near-field heat exchange between bodies held at different
temperatures
Temperature control of thermal radiation from heterogeneous bodies
We demonstrate that recent advances in nanoscale thermal transport and
temperature manipulation can be brought to bear on the problem of tailoring
thermal radiation from compact emitters. We show that wavelength-scale
composite bodies involving complicated arrangements of phase-change
chalcogenide (GST) glasses and metals or semiconductors can exhibit large
emissivities and partial directivities at mid-infrared wavelengths, a
consequence of temperature localization within the GST. We consider multiple
object topologies, including spherical, cylindrical, and mushroom-like
composites, and show that partial directivity follows from a complicated
interplay between particle shape, material dispersion, and temperature
localization. Our calculations exploit a recently developed fluctuating-volume
current formulation of electromagnetic fluctuations that rigorously captures
radiation phenomena in structures with both temperature and dielectric
inhomogeneities.Comment: 17 pages, 7 figuer
Absolute Position Total Internal Reflection Microscopy with an Optical Tweezer
A non-invasive, in-situ calibration method for Total Internal Reflection
Microscopy (TIRM) based on optical tweezing is presented which greatly expands
the capabilities of this technique. We show that by making only simple
modifications to the basic TIRM sensing setup and procedure, a probe particle's
absolute position relative to a dielectric interface may be known with better
than 10 nm precision out to a distance greater than 1 m from the surface.
This represents an approximate 10x improvement in error and 3x improvement in
measurement range over conventional TIRM methods. The technique's advantage is
in the direct measurement of the probe particle's scattering intensity vs.
height profile in-situ, rather than relying on calculations or inexact system
analogs for calibration. To demonstrate the improved versatility of the TIRM
method in terms of tunability, precision, and range, we show our results for
the hindered near-wall diffusion coefficient for a spherical dielectric
particle.Comment: 10 pages. Submitted for peer review 8/20/201
Enhanced nonlinear frequency conversion and Purcell enhancement at exceptional points
We derive analytical formulas quantifying radiative emission from
subwavelength emitters embedded in triply resonant nonlinear
cavities supporting exceptional points (EP) made of dark and leaky modes. We
show that the up-converted radiation rate in such a system can be greatly
enhanced---by up to two orders of magnitude---compared to typical Purcell
factors achievable in non-degenerate cavities, for both monochromatic and
broadband emitters. We provide a proof-of-concept demonstration by studying an
inverse-designed 2D photonic-crystal slab that supports an EP formed out of a
Dirac cone at the emission frequency and a phase-matched, leaky-mode resonance
at the second harmonic frequency
The effectiveness of thin films in lieu of hyperbolic metamaterials in the near field
We show that the near-field functionality of hyperbolic metamaterials (HMM),
typically proposed for increasing the photonic local density of states (LDOS),
can be achieved with thin metal films. Although HMMs have an infinite density
of internally-propagating plane-wave states, the external coupling to nearby
emitters is severely restricted. We show analytically that properly designed
thin films, of thicknesses comparable to the metal size of a hyperbolic
metamaterial, yield a LDOS as high as (if not higher than) that of HMMs. We
illustrate these ideas by performing exact numerical computations of the LDOS
of multilayer HMMs, along with their application to the problem of maximizing
near-field heat transfer, to show that thin films are suitable replacements in
both cases.Comment: 5 pages, 3 figure
Non-additivity of van der Waals forces on liquid surfaces
We present an approach for modeling nanoscale wetting and dewetting of liquid
surfaces that exploits recently developed, sophisticated techniques for
computing van der Waals (vdW) or (more generally) Casimir forces in arbitrary
geometries. We solve the variational formulation of the Young--Laplace equation
to predict the equilibrium shapes of fluid--vacuum interfaces near solid
gratings and show that the non-additivity of vdW interactions can have a
significant impact on the shape and wetting properties of the liquid surface,
leading to very different surface profiles and wetting transitions compared to
predictions based on commonly employed additive approximations, such as Hamaker
or Derjaguin approximations.Comment: 5 pages (including abstract, acknowledgments, and references), 3
figure
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